Understanding why replacing I3−/I− by cobalt(ii)/(iii) electrolytes in bis(diimine)copper(i)-based dye-sensitized solar cells improves performance. Issue 33 (8th August 2016)

• Record Type: Journal Article
• Authors: Fürer, Sebastian O.; Bozic-Weber, Biljana; Schefer, Thomas; Wobill, Cedric; Constable, Edwin C.; Housecroft, Catherine E.; Willgert, Markus
• Is Part Of: Journal of materials chemistry. Volume 4:Issue 33(2016)
• Page Start: 12995
• Page End: 13004
• Publication Date: 2016-08-08
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c6ta04879j
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Copper(i )-based DSCs show superior performances (reaching a PEC of 3.69%) when [Co(phen)3 ] 2+/3+ or [Co(bpy)3 ] 2+/3+ redox mediators replace I3 − /I − due to higher chemical capacitance, J SC and V OC ; the higher mass transport of [Co(phen)3 ] 2+/3+ vs. [Co(bpy)3 ] 2+/3+ leads to lower J SC, fill factor and PEC for the former vs. the latter. Abstract : The performances of dye-sensitized solar cells (DSCs) comprising heteroleptic bis(diimine)copper(i ) based dyes combined with either [Co(bpy)3 ] 2+/3+, [Co(phen)3 ] 2+/3+ or I3 − /I − redox mediators (bpy = 2, 2′-bipyridine, phen = 1, 10-phenanthroline) have been evaluated. The copper(i ) dyes contain the anchoring ligand ((6, 6′-dimethyl-[2, 2′-bipyridine]-4, 4′-diyl)bis(4, 1-phenylene))bis(phosphonic acid), 1, and an ancillary ligand (2, 3 or4 ) with a 2, 9-dimethyl-1, 10-phenanthroline metal-binding domain. Ligands2 and3 include imidazole 2′-functionalities with 4-(diphenylamino)phenyl (2 ) or 4-(bis(4- n -butoxy)phenylamino)phenyl (3 ) domains; in4, the phen unit is substituted in the 4, 7-positions with hole-transporting 4-(diphenylamino)phenyl groups. The photoconversion efficiency, η, of each of [Cu(1 )(2 )] +, [Cu(1 )(3 )] + and [Cu(1 )(4 )] + considerably improves by replacing the I3 − /I − electrolyte by [Co(bpy)3 ] 2+/3+ or [Co(phen)3 ] 2+/3+, and after a change of electrolyte solvent (MeCN to 3-methoxypropionitrile). Due to the faster charge transfer kinetics and more positive redox potential, the cobalt-based electrolytes are superior to the I3 − /I − electrolyte in terms of open-circuit voltage ( V OC ), short-circuit current ( J SC ) and η ; values of V OC = 594 mV, J SC = 9.58 mA cm −2 and η = 3.69% (relative to η = 7.12% for N719) are achieved for the best performing DSC which contains [Cu(1 )(4 )] + and [Co(bpy)3 ] 2+/3+ . Corresponding values for [Cu(1 )(4 )] + and I3 − /I − DSCs are 570–580 mV, 5.98–6.37 mA cm −2 and 2.43–2.62%. Electrochemical impedance spectroscopy (EIS) has been used to study DSCs with [Cu(1 )(4 )] + and the three electrolytes. EIS shows that the DSC with I3 − /I − has the highest recombination resistance, whereas the [Co(phen)3 ] 2+/3+ electrolyte gives the highest chemical capacitance and V OC and, between [Co(bpy)3 ] 2+/3+ and [Co(phen)3 ] 2+/3+, the higher recombination resistance. The [Co(phen)3 ] 2+/3+ electrolyte exhibits the highest mass transport restrictions which result in a lower J SC and DSC efficiency compared to the [Co(bpy)3 ] 2+/3+ electrolyte.